3D landslide run out modelling using the Particle Flow Code PFC3D

Rockfalls are modelled as the movements of single rock blocks over a surface or as the movement of a viscous mass over a surface (e.g. DAN). In reality a mass of discrete, interacting rock blocks is moving downslope. Thus the program PFC (Particle Flow Code) based on the Distinct Element Method was modified in order to model rock mass falls realistically in 3 dimensions based on physical relations. PFC models the movement and interaction of circular (2D) or spherical (3D) particles and wall elements using the laws of motion and of force-displacement. In the course of the calculation the contacts between particles and particles or particles and walls are detected automatically. The particles may be bonded together at their contact points, and the bondage can break due to an impact. For realistic modelling of the run out a viscous damping routine in case of a particle-wall contact was introduced. Numerical drop tests and back analyses of several rock mass falls provided appropriate damping factors. Thus, the movement types bouncing, sliding, rolling and free failing of single rock blocks and the interaction between the blocks occurring in a rock mass fall can be modelled realistically by using the adapted code of PFC. The application of this method is demonstrated by the example of Aaknes (Western Norway).